A projection-type image display device that collects white light from a light source and forms a light-emitting surface, has a rotation-type color filter arranged in the vicinity of the light-emitting surface, collects outgoing light from the color filter and allows the outgoing light to enter one sheet of optical modulation element, and projects an image formed in the optical modulation element, onto a screen through a projecting lens, is already known in PATENT LITERATURE 1 below and the like. Further, it is already known in PATENT LITERATURE 2 below that, in the projection-type image display device (or a liquid crystal display device), employing a square rod lens with a cross section having a similar figure to a display area of a display panel, in order to efficiently irradiate the display area of the display panel with the light from the light source, and having the rod lens configured from a group of a plurality of (four) divided rods around an optical axis thereof, in order to make an optical path length from a light source unit to an image display element short, thereby to downsize the entire device.